Agent prioritization for autonomous vehicles

ABSTRACT

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for identifying high-priority agents in the vicinity of a vehicle. In one aspect, a method comprises processing an input that characterizes a trajectory of the vehicle in an environment using an importance scoring model to generate an output that defines a respective importance score for each of a plurality of agents in the environment in the vicinity of the vehicle. The importance score for an agent characterizes an estimated impact of the agent on planning decisions generated by a planning system of the vehicle which plans a future trajectory of the vehicle. The high-priority agents are identified as a proper subset of the plurality of agents with the highest importance scores.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority to,U.S. patent application Ser. No. 16/198,130, titled “AGENTPRIORITIZATION FOR AUTONOMOUS VEHICLES,” filed on Nov. 21, 2018, and isa continuation-in-part of, and claims priority to, U.S. patentapplication Ser. No. 16/196,769, titled “TRAJECTORY REPRESENTATION INBEHAVIOR PREDICTION SYSTEMS,” filed on Nov. 20, 2018. The disclosure ofthe foregoing application is incorporated herein by reference in itsentirety for all purposes.

BACKGROUND

This specification relates to autonomous vehicles.

Autonomous vehicles include self-driving cars, boats, and aircraft.Autonomous vehicles use a variety of on-board sensors and computersystems to detect nearby objects and use such detections to make controland navigation decisions.

SUMMARY

This specification describes a system implemented as computer programson-board a vehicle that generates prediction data for agents in avicinity of the vehicle based on the estimated impacts of the agents onplanning decisions generated by a planning system of the vehicle.

According to a first aspect, there is provided a method performed by oneor more data processing apparatus, the method including: processing aninput that characterizes a trajectory of a vehicle in an environmentusing an importance scoring model to generate an output that defines arespective importance score for each of multiple agents in theenvironment in the vicinity of the vehicle, where the importance scorefor an agent characterizes an estimated impact of the agent on planningdecisions generated by a planning system of the vehicle which plans afuture trajectory of the vehicle; identifying, as high-priority agents,a proper subset of the multiple agents with the highest importancescores; for only those agents of the multiple agents that are identifiedas high-priority agents, generating data characterizing the agents usinga first prediction model; and providing the data characterizing thehigh-priority agents generated using the first prediction model to theplanning system of the vehicle to generate the planning decisions whichplan the future trajectory of the vehicle.

In some implementations, the method further includes obtaininghistorical data characterizing the trajectory of the vehicle in theenvironment, the historical data including, for each of multipleprevious time points, data defining: (i) a spatial position in theenvironment occupied by the vehicle at the previous time point, and (ii)respective values of each motion parameter in a predetermined set ofmotion parameters, where the value of each motion parametercharacterizes a respective feature of a motion of the vehicle at theprevious time point; generating a representation of the trajectory ofthe vehicle in the environment, where: the representation of thetrajectory of the vehicle in the environment is a concatenation ofmultiple channels; each channel is represented as a two-dimensionalarray of data values; each position in each channel corresponds to arespective spatial position in the environment; corresponding positionsin different channels correspond to the same spatial position in theenvironment; the channels include a time channel and a respective motionchannel corresponding to each motion parameter in the predetermined setof motion parameters; and for each particular spatial position in theenvironment occupied by the vehicle at a particular previous time point:the position in the time channel which corresponds to the particularspatial position defines the particular previous time point; and foreach motion channel, the position in the motion channel whichcorresponds to the particular spatial position defines the value of themotion parameter corresponding to the motion channel at the particularprevious time point; where processing an input that characterizes atrajectory of the vehicle in the environment includes processing aninput that includes the representation of the trajectory of the vehiclein the environment.

In some implementations, the output of the importance scoring modelincludes an output channel that is represented as a two-dimensionalarray of data values; each position in the output channel corresponds toa respective spatial position in the environment; and for each spatialposition in the environment that is occupied by an agent of the multipleagents at a current time point, the position in the output channel thatcorresponds to the spatial position defines an importance score of theagent.

In some implementations, the method further includes, for each agent ofthe multiple agents: generating a respective feature representation ofthe agent, including: generating one or more importance score featuresof the agent from the output channel; generating one or more additionalfeatures of the agent based on sensor data captured by one or moresensors of the vehicle; and generating the feature representation of theagent from the importance score features of the agent and the additionalfeatures of the agent; processing the feature representation of theagent using an importance score refining model to generate a refinedimportance score for the agent that characterizes an estimated impact ofthe agent on planning decisions generated by a planning system of thevehicle which plans a future trajectory of the vehicle.

In some implementations, obtaining the respective values of each motionparameter in the predetermined set of motion parameters for a previoustime point includes one or more of: obtaining the value of a velocitymotion parameter which characterizes a velocity of the vehicle at theprevious time point; obtaining the value of an acceleration motionparameter which characterizes an acceleration of the vehicle at theprevious time point; and obtaining the value of a heading motionparameter which characterizes a heading of the vehicle at the previoustime point.

In some implementations, the input processed by the importance scoringmodel further includes one or more of: (i) a road-graph channelrepresenting a known geometry of the environment, (ii) a vehiclelocalization channel which represents a spatial position of the vehiclein the environment at a current time point by a vehicle bounding box,and (iii) an auxiliary localization channel which represents respectivespatial positions of the multiple agents in the environment at a currenttime point by respective bounding boxes.

In some implementations, the method further includes generating a jointrepresentation of trajectories of the multiple agents in the environmentin the vicinity of the vehicle, where the input processed by theimportance scoring model further includes the joint representation ofthe trajectories of the multiple agents.

In some implementations, the joint representation of the trajectories ofthe multiple agents in the environment includes an auxiliary timechannel and a respective auxiliary motion channel corresponding to eachmotion parameter in the predetermined set of motion parameters; eachchannel is represented as a two-dimensional array of data values andeach data value in each channel corresponds to a respective spatialposition in the environment; and for each particular spatial position inthe environment occupied by a particular agent of the multiple agents ata particular previous time point: the data value in the auxiliary timechannel which corresponds to the particular spatial position defines theparticular previous time point; and for each auxiliary motion channel,the data value in the auxiliary motion channel which corresponds to theparticular spatial position defines a value of the motion parametercorresponding to the auxiliary motion channel which characterizes arespective feature of a motion of the particular agent at the particularprevious time point.

In some implementations, identifying, as high-priority agents, a propersubset of the multiple agents with the highest importance scoresincludes: identifying, as high-priority agents, a predetermined numberof the multiple agents with the highest importance scores.

In some implementations, the method further includes: for one or more ofthe multiple agents that are not identified as high-priority agents,generating data characterizing the one or more agents using a secondprediction model, where the first prediction model has a first number ofmodel parameters, the second prediction model has a second number ofmodel parameters, and the first number of model parameters is greaterthan the second number of model parameters; and providing the datacharacterizing the one or more agents generated using the secondprediction model to the planning system in addition to the datacharacterizing the high priority agents generated using the firstprediction model.

According to a second aspect, there is provided a method, performed byone or more data processing apparatus, for training an importancescoring model, where the importance scoring model is configured toprocess a feature representation of an agent in a vicinity of a vehicleto generate an importance score for the agent, where the importancescore for the agent characterizes an impact of the agent on planningdecisions generated by a planning system of the vehicle which plans afuture trajectory of the vehicle, the method including: generatingmultiple training examples, where each given training example includes:(i) respective feature representations of multiple given agents in agiven vicinity of a given vehicle at a given time point, and (ii) datadefining a given ranking of the given agents in the given vicinity ofthe given vehicle in order of their impact on given planning decisionsgenerated by a given planning system which plans a future trajectory ofthe given vehicle, where generating a particular training exampleincludes: for each of multiple particular agents in a particularvicinity of a particular vehicle at a particular time point, generatingrespective data characterizing a predicted future behavior of theparticular agent using a behavior prediction system (e.g., neuralnetwork); providing, for each of the particular agents in the particularvicinity of the particular vehicle at the particular time point, therespective data characterizing the predicted future behavior of theparticular agent to a particular planning system; receiving, from theparticular planning system, particular planning decisions which plan afuture trajectory of the particular vehicle; and determining, based onthe particular planning decisions, a particular ranking of theparticular agents in the particular vicinity of the particular vehicleat the particular time point in order of their impact on the particularplanning decisions; and training the importance scoring model based onthe training examples, including, for each given training example:training the importance scoring model to generate respective importancescores for the given agents characterized by the given training examplethat conform to the given ranking specified by the given trainingexample.

In some implementations, generating training examples includesgenerating the training examples based on real or simulated driving datalogs.

In some implementations, training the importance scoring model togenerate respective importance scores for the given agents characterizedby the given training example that conform to the given rankingspecified by the given training example includes: processing a firstfeature representation of a first agent characterized by the giventraining example to generate a first importance score; processing asecond feature representation of a second agent characterized by thegiven training example to generate a second importance score;determining a loss based on whether the first importance score and thesecond importance score conform to the given ranking specified by thegiven training example; and updating current parameter values of theimportance scoring model based on the loss.

In some implementations, each of the particular planning decisions whichplan the future trajectory of the particular vehicle include: (i) anaction to be performed by the particular vehicle, and (ii) a particularagent in the particular vicinity of the particular vehicle which promptsthe particular planning system to generate the particular planningdecision.

In some implementations, determining, based on the particular planningdecisions, a particular ranking of the particular agents in theparticular vicinity of the particular vehicle at the particular timepoint in order of their impact on the particular planning decisionsincludes: determining a respective planning score for each particularagent based on any actions which the particular agent prompts theparticular planning system to generate; and determining the particularranking of the particular agents based on the respective planning scoresof the particular agents.

In some implementations, each training example includes respectivefeature representations of every agent in the vicinity of the vehiclethat is detected by an object detection system of the vehicle.

In some implementations, the given ranking of the given agents defines:(i) a partition of the given agents into multiple groups, where eachgroup includes one or more given agents, and (ii) for each pair ofgroups including a first group and a second group, whether the givenagents in the first group have a greater impact on the given planningdecisions than the given agents in the second group.

According to a third aspect, there are provided one or morenon-transitory computer storage media storing instructions that whenexecuted by one or more computers cause the one or more computers toperform operations including the operations of the previously describedmethods.

According to a fourth aspect, there is provided a system, including adata processing apparatus; and a memory in data communication with thedata processing apparatus and storing instructions that cause the dataprocessing apparatus to perform operations including the operations ofthe previously described methods.

Particular embodiments of the subject matter described in thisspecification can be implemented so as to realize one or more of thefollowing advantages.

In order for a planning system of a vehicle to generate planningdecisions which cause the vehicle to travel along a safe and comfortabletrajectory, the planning system must be provided with timely andaccurate prediction data (e.g., behavior prediction data) for the agentsin the vicinity of the vehicle. However, generating prediction data foran agent in the vicinity of the vehicle may require substantialcomputational resources (e.g., memory, computing power, or both). Incertain situations, a large number of other agents in the environmentmay be in the vicinity of the vehicle (e.g., when the vehicle istraveling along a busy highway). In these situations, the limitedcomputational resources available on-board the vehicle may beinsufficient to generate timely prediction data for all the agents inthe vicinity of the vehicle.

The on-board system described in this specification can concentrate thelimited computational resources available on-board the vehicle (e.g.,memory, computing power, or both) on generating precise prediction datafor only those agents which are likely to have the biggest impact on theplanning decisions generated by the planning system. The system cangenerate prediction data for the remaining “low-priority” agents using amore computationally efficient prediction model. In this manner, theon-board system described in this specification can generate timelyprediction data which enables the planning system to generate planningdecisions that cause the vehicle to travel along a safe and comfortabletrajectory despite the limited computational resources availableon-board the vehicle.

The on-board system described in this specification uses a datarepresentation system to generate trajectory representation data whichdefines the trajectory of a vehicle and the trajectories of one or moreagents as a collection of two-dimensional (2D) “channels”. The on-boardsystem can process the trajectory representation data using aconvolutional neural network to generate an output that definesrespective importance scores for each of the agents. The representationof the trajectories as a collection of 2D channels is more compact thana representation as a collection of 3D channels and, unlike a 1Drepresentation, can be processed by multi-dimensional convolutionalfilters in the convolutional neural network. Therefore, the on-boardsystem may consume fewer computational resources (e.g., memory,computing power, or both) by representing the trajectories as acollection of 2D channels than would be the case if the on-board systemrepresented the trajectories as a collection of 3D channels. Moreover,the convolutional neural network can learn to exploit complexinteractions between different spatial regions of the trajectoryrepresentation data by processing the collection of 2D channelsrepresenting the trajectories using multi-dimensional convolutionalfilters and thereby generate more accurate importance scores.

The on-board system described in this specification can processimportance scores generated using an importance scoring model (i.e.,that processes trajectory representation data represented as acollection of 2D channels) and additional features based on sensor datacaptured by the sensors of the vehicle to generate “refined” importancescores. The refined importance scores may be more accurate than theimportance scores generated by the importance scoring model.

The details of one or more embodiments of the subject matter of thisspecification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example on-board system.

FIG. 2 is a block diagram of an example importance scoring system and anexample prediction system.

FIG. 3 is a block diagram of an example data representation system.

FIG. 4 is an illustration of an example process by which the datarepresentation system can generate a vehicle time channel, a vehiclevelocity channel, and a vehicle heading channel.

FIG. 5 is a flow diagram of an example process for generating predictiondata to be provided to a planning system.

FIG. 6 is a flow diagram of an example process for generating a trainingexample which can be used to train an importance scoring model.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

This specification describes how an on-board system of a vehicle cangenerate prediction data (e.g., behavior prediction data) for agents inthe vicinity of the vehicle. The agents in the vicinity of the vehiclemay be, for example, pedestrians, bicyclists, or other vehicles. Togenerate the prediction data, the on-board system determines arespective importance score for each agent in the vicinity of thevehicle. The importance score for an agent characterizes an estimatedimpact of the agent on planning decisions generated by a planning systemof the vehicle which plan the future trajectory of the vehicle. Theon-board system identifies which of the agents in the vicinity of thevehicle are “high-priority” agents based on the importance scores, andgenerates precise prediction data for these high-priority agents using aprediction model. For the remaining agents in the vicinity of thevehicle which are not high-priority agents, the on-board system can useless computationally-intensive (but potentially less precise) predictionmodels to generate prediction data. Alternatively, the on-board systemmay refrain from generating prediction data for some or all of theagents that are not determined to be high-priority agents. Thesefeatures and other features are described in more detail below.

FIG. 1 is a block diagram of an example on-board system 100. Theon-board system 100 is composed of hardware and software components,some or all of which are physically located on-board a vehicle 102. Insome cases, the on-board system 100 can generate planning decisionswhich plan the future trajectory of the vehicle 102, present informationto the driver of the vehicle 102 to assist the driver in operating thevehicle safely, or both. For example, in response to determining thatthe trajectory of another vehicle is likely to cross the trajectory ofthe vehicle 102, the on-board system 100 may generate planning decisionswhich adjust the future trajectory of the vehicle 102 to avoid acollision (e.g., by braking). As another example, in response todetermining that the trajectory of another vehicle is likely to crossthe trajectory of the vehicle 102, the on-board system 100 may presentan alert message which prompts the driver of the vehicle 102 to adjustthe trajectory of the vehicle 102 to avoid a collision.

Although the vehicle 102 in FIG. 1 is depicted as an automobile, and theexamples in this specification are described with reference toautomobiles, in general the vehicle 102 can be any kind of vehicle. Forexample, besides an automobile, the vehicle 102 can be a watercraft oran aircraft. Moreover, the on-board system 100 can include componentsadditional to those depicted in FIG. 1 (e.g., a collision detectionsystem or a navigation system).

The on-board system 100 includes a sensor system 104 which enables theon-board system 100 to “see” the environment in the vicinity of thevehicle 102. More specifically, the sensor system 104 includes one ormore sensors, some of which are configured to receive reflections ofelectromagnetic radiation from the environment in the vicinity of thevehicle 102. For example, the sensor system 104 can include one or morelaser sensors (e.g., LIDAR laser sensors) that are configured to detectreflections of laser light. As another example, the sensor system 104can include one or more radar sensors that are configured to detectreflections of radio waves. As another example, the sensor system 104can include one or more camera sensors that are configured to detectreflections of visible light.

The sensor system 104 continually (i.e., at each of multiple timepoints) captures raw sensor data which can indicate the directions,intensities, and distances travelled by reflected radiation. Forexample, a sensor in the sensor system 104 can transmit one or morepulses of electromagnetic radiation in a particular direction and canmeasure the intensity of any reflections as well as the time that thereflection was received. A distance can be computed by determining thetime which elapses between transmitting a pulse and receiving itsreflection. Each sensor can continually sweep a particular space inangle, azimuth, or both. Sweeping in azimuth, for example, can allow asensor to detect multiple objects along the same line of sight.

The on-board system 100 can use the sensor data continually generated bythe sensor system 104 to track the trajectories of agents (e.g.,pedestrians, bicyclists, other vehicles, and the like) in theenvironment in the vicinity of the vehicle 102. The trajectory of anagent refers to data defining, for each of multiple time points, thespatial position occupied by the agent in the environment at the timepoint and characteristics of the motion of the agent at the time point.The characteristics of the motion of an agent at a time point caninclude, for example, the velocity of the agent (e.g., measured in milesper hour—mph), the acceleration of the agent (e.g., measured in feet persecond squared), and the heading of the agent (e.g., measured indegrees). The heading of an agent refers to the direction of travel ofthe agent and can be expressed as angular data (e.g., in the range 0degrees to 360 degrees) which is defined relative to a given frame ofreference in the environment (e.g., a North-South-East-West frame ofreference).

To track the trajectory of an agent in the environment in the vicinityof the vehicle 102, the on-board system 100 can maintain (e.g., in aphysical data storage device) historical data defining the trajectory ofthe agent up to the current time point. The on-board system 100 can usethe sensor data continually generated by the sensor system 104 tocontinually update (e.g., every 0.1 seconds) the historical datadefining the trajectory of the agent. At a given time point, thehistorical data may include data defining: (i) the respectivetrajectories of agents in the vicinity of the vehicle 102, and (ii) thetrajectory of the vehicle 102 itself, up to the given time point.

At any given time point, one or more agents in the environment may be inthe vicinity of the vehicle 102. The agents in the vicinity of thevehicle 102 may be, for example, pedestrians, bicyclists, or othervehicles. The on-board system 100 uses a prediction system 106 tocontinually (i.e., at each of multiple time points) generate predictiondata 108 which characterizes some or all of the agents in the vicinityof the vehicle 102. For example, for each of multiple agents in thevicinity of the vehicle 102, the prediction data 108 may be behaviorprediction data which defines respective probabilities that the agentmakes each of a predetermined number of possible driving decisions(e.g., yielding, changing lanes, passing, braking, or accelerating). Asanother example, for each of the multiple agents in the vicinity of thevehicle 102, the prediction data 108 may be classification predictiondata which defines respective probabilities that the agent is each of apredetermined number of possible agent types (e.g., animal, pedestrian,bicyclist, car, or truck).

The on-board system 100 can provide the prediction data 108 generated bythe prediction system 106 to a planning system 110, a user interfacesystem 112, or both.

When the planning system 110 receives the prediction data 108, theplanning system 110 can use the prediction data 108 to generate planningdecisions 144 which plan the future trajectory of the vehicle 102. Theplanning decisions 144 generated by the planning system 110 can include,for example: yielding (e.g., to pedestrians), stopping (e.g., at a“Stop” sign), passing other vehicles, adjusting vehicle lane position toaccommodate a bicyclist, slowing down in a school or construction zone,merging (e.g., onto a highway), and parking. In a particular example,the on-board system 100 may provide the planning system 110 withbehavior prediction data indicating that the future trajectory ofanother vehicle is likely to cross the future trajectory of the vehicle102, potentially resulting in a collision. In this example, the planningsystem 110 can generate a planning decision 144 to apply the brakes ofthe vehicle 102 to avoid a collision.

The planning decisions 144 generated by the planning system 110 can beprovided to a control system 142 of the vehicle 102. The control system142 of the vehicle can control some or all of the operations of thevehicle by implementing the planning decisions 144 generated by theplanning system. For example, in response to receiving a planningdecision 144 to apply the brakes of the vehicle, the control system 142of the vehicle 102 may transmit an electronic signal to a brakingcontrol unit of the vehicle. In response to receiving the electronicsignal, the braking control unit can mechanically apply the brakes ofthe vehicle.

When the user interface system 112 receives the prediction data 108, theuser interface system 112 can use the prediction data 108 to presentinformation to the driver of the vehicle 102 to assist the driver inoperating the vehicle 102 safely. The user interface system 112 canpresent information to the driver of the vehicle 102 by any appropriatemeans, for example, by an audio message transmitted through a speakersystem of the vehicle 102 or by alerts displayed on a visual displaysystem in the vehicle (e.g., an LCD display on the dashboard of thevehicle 102). In a particular example, the on-board system 100 mayprovide the user interface system 112 with prediction data 108indicating that the future trajectory of another vehicle is likely tocross the future trajectory of the vehicle 102, potentially resulting ina collision. In this example, the user interface system 112 can presentan alert message to the driver of the vehicle 102 with instructions toadjust the trajectory of the vehicle 102 to avoid a collision.

In order for the planning system 110 to generate planning decisionswhich cause the vehicle 102 to travel along a safe and comfortabletrajectory, the on-board system 100 must provide the planning system 110with timely and accurate prediction data 108. However, the predictionsystem 106 may require substantial computational resources (e.g.,memory, computing power, or both) to generate prediction data 108 for anagent in the vicinity of the vehicle. In certain situations, a largenumber of other agents in the environment may be in the vicinity of thevehicle 102 (e.g., when the vehicle 102 is traveling along a busyhighway). In these situations, the limited computational resourcesavailable on-board the vehicle 102 may be insufficient for theprediction system 106 to generate timely prediction data 108 for all theagents in the vicinity of the vehicle 102.

To enable the prediction system 106 to generate timely prediction data108, the on-board system 100 can identify one or more of the agents inthe vicinity of the vehicle 102 as “high-priority” agents. In somecases, the on-board system 100 identifies only a fraction of the agentsin the vicinity of the vehicle 102 as high-priority agents. Theprediction system 106 is then configured to generate precise predictiondata 108 for the high-priority agents using a prediction model (e.g., aprediction neural network). The prediction system 106 can generateprediction data 108 for any remaining agents which are not identified ashigh-priority agents, and which will be referred to in thisspecification as “low-priority” agents, using less computationallyintensive (but potentially less precise) behavior prediction models.Alternatively, the on-board system 100 may refrain from generating anyprediction data 108 for some or all of the low-priority agents. In thisspecification, a “prediction model” should be understood as implementinga prediction algorithm.

The on-board system 100 determines which of the agents in the vicinityof the vehicle 102 to designate as high-priority agents using animportance scoring system 114. The importance scoring system 114 isconfigured to generate a respective importance score 116 for each agentin the vicinity of the vehicle 102 using an importance scoring model.The importance scoring model can be implemented, for example, as aneural network model, a random forest model, a support vector machine(SVM) model, or as any other type of trainable machine learning model.

More specifically, the importance scoring model is configured to processan input that includes data characterizing the trajectory of the vehicle102 (and, optionally, the trajectories of one or more agents in thevicinity of the vehicle 102) in accordance with trained parameter valuesof the importance scoring model to generate an output that defines theimportance scores 116 for the agents in the vicinity of the vehicle. Theimportance score 116 for an agent characterizes an estimated impact ofthe agent on the planning decisions generated by the planning system 110which plan the future trajectory of the vehicle 102. After generatingthe importance scores 116, the on-board system 100 can determine one ormore of the agents in the vicinity of the vehicle with the highestimportance scores to be high-priority agents.

In a particular example, at a particular intersection there may be: (i)an oncoming vehicle which may turn into the path of the vehicle 102, and(ii) a bicyclist which is far behind the vehicle 102 and unlikely toaffect the planning decisions of the planning system 110. In thisexample, the importance scoring system 114 may generate a higherimportance score for the oncoming vehicle than for the bicyclist,potentially causing the oncoming vehicle to be designated ahigh-priority agent and the bicyclist a low-priority agent.

By generating prediction data 108 based on the importance scores 116,the on-board system 100 can concentrate its limited computationalresources on generating precise prediction data 108 for only thoseagents which are likely to have the biggest impact on the planningdecisions generated by the planning system 110. In this manner, theon-board system 100 can generate timely prediction data 108 whichenables the planning system 110 to generate planning decisions thatcause the vehicle to travel along a safe and comfortable trajectorydespite the limited computational resources available on-board thevehicle 102.

In some cases, the on-board system 100 can provide the importance scores116 directly to the planning system 110. The planning system 110 can usethe importance scores 116 by, for example, allocating a greater amountof computational resources to processing data characterizing thehigh-priority agents than the low-priority agents in generating theplanning decisions 144. More generally, any processing module of theon-board system (including but not limited to the prediction system 106and the planning system 110) can use the importance scores 116 toallocate a greater amount of computational resources to processing datacharacterizing the high-priority agents than the low-priority agents.

To allow the importance scoring system 114 to accurately prioritizeagents, a training system 120 can determine trained parameter values 122of the importance scoring model included in the importance scoringsystem 114. The training system 120 is typically hosted within a datacenter 124, which can be a distributed computing system having hundredsor thousands of computers in one or more locations.

The training system 120 includes a training importance scoring model 126that is configured to process an input that includes data characterizingthe trajectory of a vehicle to generate an output that definescorresponding importance scores 140 for agents in the vicinity of thevehicle. The training system 120 includes multiple computing deviceshaving software or hardware modules that implement the operations of thetraining importance scoring model 126. For example, if the trainingimportance scoring model 126 is an importance scoring neural network,then the training system 120 includes multiple computing devices havingsoftware or hardware modules that implement the respective operations ofeach layer of the training importance scoring neural network accordingto an architecture of the training importance scoring neural network.The training importance scoring model 126 is generally the same model(or almost the same model) as the on-board importance scoring model. Forexample, if the training importance scoring model is a neural network,then it generally has (at least partially) the same architecture as theon-board importance scoring neural network included in the importancescoring system 114.

The training importance scoring model 126 can compute the operations ofthe training importance scoring model 126 using current values ofparameters 128 stored in a collection of model parameters 130. Althoughillustrated as being logically separated, the model parameters 130 andthe software or hardware modules performing the operations may actuallybe located on the same computing device or on the same memory device.

The training system 120 trains the training importance scoring model 126using a training data set 132 which includes multiple training examples134. The training examples 134 may be obtained from real or simulateddriving logs. Each of the training examples 134 may include: (i) aninput of the training importance scoring model including trajectoryrepresentation data characterizing the trajectory of a vehicle at arespective time point (and, optionally, the trajectories of agents inthe vicinity of the vehicle), and (ii) a label defining a ranking of theagents in order of their impact on planning decisions generated by aplanning system of the vehicle. An example process for generatingtraining examples 134 is described with reference to FIG. 6. An exampledata representation system for generating trajectory representation datais described in more detail with reference to FIG. 3.

The training importance scoring model 126 can process the inputs fromthe training examples 134 to generate, for each training example 134, anoutput which defines respective importance scores 140. A training engine136 compares importance scores 140 to the ranking of the agents definedby the labels in the training examples 134. For example, when thetraining importance scoring model 126 is a neural network, the trainingengine 136 can compute gradients of a loss function that characterizesdiscrepancies between the importance scores 140 and the ranking of theagents defined by the labels in the training examples 134. The trainingengine 126 can use the gradients to generate updated model parameters138.

In a particular example, the training importance scoring model 126 maybe configured to generate an output that includes an output channel thatis represented as a two-dimensional array of data values. Each positionin the output channel corresponds to a respective spatial position inthe environment. For each spatial position in the environment that isoccupied by an agent, the position in the output channel thatcorresponds to the spatial position defines an importance score for theagent. The importance score for an agent may be a probability value(e.g., a numerical value between 0 and 1) that indicates a probabilitythat the agent is a “high-priority” agent. For each training example,the label defining the ranking of the agents may define whether each ofthe agents is a “high-priority” agent or a “low-priority” agent. In thisexample, the loss function may be a cross-entropy classification lossfunction based on whether the importance scores defined by the output ofthe training importance scoring model accurately classify whether eachagent is a high-priority agent.

The training engine 136 generates updated model parameter values 138 byusing an appropriate machine learning training technique (e.g.,stochastic gradient descent). The training engine 136 can then updatethe collection of model parameters 130 using the updated model parametervalues 138.

In some cases, as will be described further with reference to FIG. 5,the on-board system may include an importance score refining model. Theimportance score refining model is configured to process featurerepresentations of each agent (that include “importance score features”generated based on the output of the importance scoring model) togenerate “refined” importance scores that may be more accurate than theoriginal importance scores. The importance score refining model can betrained in a similar manner as the importance scoring model. In aparticular example, the loss function for the importance score refiningmodel may characterize whether the ranking of pairs of agents defined bythe refined importance scores are consistent with the ranking of thepairs of agents defined by the labels in the training examples.

After training is complete, the training system 120 can provide a set oftrained parameter values 122 to the on-board system 100 for use ingenerating importance scores that enable the generation of timely andaccurate behavior prediction data 108. The training system 120 canprovide the set of trained parameter values 122 by a wired or wirelessconnection to the on-board system 100.

FIG. 2 is a block diagram of an example importance scoring system 114and an example prediction system 106. The importance scoring system 114and the prediction system 106 are examples of systems implemented ascomputer programs on one or more computers in one or more locations inwhich the systems, components, and techniques described below areimplemented.

The importance scoring system 114 is configured to process historicaldata 202 (generated by the sensor system 104 of the vehicle 102) whichcharacterizes at least the trajectory of the vehicle 102 (and,optionally, the trajectories of agents in the vicinity of the vehicle102) to generate a respective importance score 204 for each agent in thevicinity of the vehicle 102. The importance score 204 for an agentcharacterizes an estimated impact of the agent on planning decisionsgenerated by the planning system of the vehicle 102 which plan thefuture trajectory of the vehicle 102.

In a particular example depicted in FIG. 2, the environment 206 is aroadway and two vehicles, denoted Agent A and Agent B, are in thevicinity of the vehicle 102. Agent A is maneuvering to cut in front ofthe vehicle 102, while Agent B is travelling parallel to the vehicle102. In this example, the importance scoring system 114 may assign ahigher importance score to Agent A than to Agent B, specifically,because Agent A is likely to have a greater impact on the planningdecisions generated by the planning system 110 of the vehicle 102. Forexample, the planning system 110 of the vehicle 102 may generateplanning decisions which cause the vehicle 102 to brake to avoid acollision with Agent A. In one example, the importance scoring system114 may generate an importance score of 0.9 for Agent A, and animportance score of 0.65 for Agent B.

To generate the importance scores 204, the importance scoring system 114processes the historical data 202 using a data representation system 208which is configured to generate trajectory representation data 210. Aswill be described in more detail with reference to FIG. 3, thetrajectory representation data 210 includes a representation of thetrajectory of the vehicle 102 up to the current time point. Optionally,the trajectory representation data 210 can further include one or moreof: (i) representations of the trajectories of the agents in thevicinity of the vehicle up to the current time point, (ii) arepresentation of a candidate future trajectory of the vehicle after thecurrent time point, or (iii) representations of predicted futuretrajectories of the one or more agents after the current time point. Insome cases, the representations of trajectories of the other agents inthe vicinity of the vehicle may be a joint representation.

The importance scoring system 114 processes the trajectoryrepresentation 210 using an importance scoring model 212 to generate anoutput that defines a respective importance score 204 for each of theagents in the vicinity of the vehicle 102. For example, the importancesoring model 212 may generate an output that includes an output channelrepresented as a 2D array of data values. In this example, each positionin the output channel corresponds to a respective spatial position inthe environment. For each spatial position in the environment that isoccupied by an agent, the position in the output channel thatcorresponds to the spatial position defines an importance score for theagent. In a particular example, 214 depicts an output channelcorresponding to the example environment 206 depicted in FIG. 2. In thisexample, the spatial position 216 in the output channel corresponds tothe Agent A in the environment 206 and has value 0.9, while spatialposition 218 in the output channel corresponds to Agent B in theenvironment 206 and has value 0.65.

In some cases, the importance scoring system 114 processes one or more“additional features” (i.e., in addition to the trajectoryrepresentation 210) based on the sensor data captured by the sensors ofthe vehicle. For example, for each agent, the additional features mayinclude: (1) the distance of the agent from the vehicle, (2) whether theagent is in front of the vehicle, (3) the current speed of the agent,(4) the current acceleration of the agent, (5) a type of the agent(e.g., cyclist, car, pedestrian, or child), (6) the distance of theagent from a candidate future trajectory of the vehicle, (7) an amountof time until the candidate future trajectory of the vehicle is closestto the agent, (8) an amount of time until the predicted futuretrajectory of the agent intersects the candidate future trajectory ofthe vehicle, and (9) the minimum time for the agent to collide with thevehicle if no action is taken. The additional features may berepresented as a vector of numerical values (or in any other appropriateformat).

Each of the importance scores 204 is represented as a respectivenumerical value. The importance scoring model 212 can be implemented asany appropriate model, for example, as a neural network (with anyappropriate architecture), a random forest, or a support vector machine.

The importance scores 204 generated by the importance scoring system 114are used by the prediction system 106 to generate prediction data 220which characterizes one or more agents in the vicinity of the vehicle.For example, the prediction data 220 may be behavior prediction datawhich characterizes the predicted future behavior of one or more of theagents in the vicinity of the vehicle 102. In this example, for one ormore of the agents in the vicinity of the vehicle 102, the predictiondata 220 may define respective probabilities that the agent makes eachof a predetermined number of possible driving decisions (e.g., yielding,changing lanes, passing, braking, or accelerating). As another example,the prediction data 220 may be classification prediction data whichdefines respective probabilities that the agent is each of apredetermined number of possible agent types (e.g., animal, pedestrian,bicyclist, car, or truck). Further examples of prediction data aredescribed with reference to FIG. 5.

The prediction system 106 processes the importance scores 204 using aranking engine 222 to identify which (if any) of the agents in thevicinity of the vehicle 102 are high-priority agents. For example, theranking engine 222 may identify each agent with an importance score thatsatisfies a predetermined threshold as a high-priority agent. In aparticular example, the ranking engine may identify each agent with animportance score that exceeds the predetermined threshold of 0.8 as ahigh-priority agent. As another example, the ranking engine 222 mayidentify a predetermined number of the agents with the highestimportance scores as high-priority agents. In a particular example, theranking engine 222 may identify the three agents with the highestimportance scores as high priority agents. As another example, theranking engine may identify a dynamically determined number of agentswith the highest importance scores as high-priority agents based on thecomputational resources currently available on-board the vehicle forbehavior prediction.

After identifying the high-priority agents 224, the prediction system106 uses a high-priority prediction model 226 to generate respectiveprediction data 220 for each of the high-priority agents 224. Thehigh-priority prediction model 226 may generate prediction data 220 foran agent by, for example, processing a representation of the trajectoryof the agent up to the current time point using a prediction neuralnetwork.

The prediction system 106 can use low-priority prediction models 228 togenerate respective prediction data 220 for each of the remainder of theagents which the ranking engine 222 does not identify as high-priorityagents 224 (i.e., the low-priority agents 230). In some cases, theprediction system 106 processes each of the low-priority agents 230 withthe same low-priority prediction model. In some cases, the predictionsystem 106 includes multiple low-priority prediction models withdifferent numbers of model parameters, and processes low-priority agentsthat have higher importance scores with low-priority behavior predictionmodels with more model parameters. Generally, the high-priorityprediction model 226 has a greater number of model parameters than thelow-priority prediction model 228, and can therefore generate moreprecise prediction data 220 than the low-priority prediction model 228.However, the low-priority prediction model 228 may consume fewercomputational resources (e.g., memory, computing power, or both) thanthe high-priority prediction model 226. In a particular example, thehigh-priority prediction model 226 may be implemented as a deep neuralnetwork with thousands of model parameters, while the low-priorityprediction model 228 may be implemented as a linear model with tens orhundreds of model parameters.

In some cases, the prediction system 106 may refrain from generatingprediction data 220 for some or all of the low-priority agents 230. Forexample, the prediction system 106 may postpone generating behaviorprediction data for the low-priority agents 230 until a later time pointwhen more computational resources are available. In these examples, theprediction system 106 may require that prediction data be generated foreach of the agents in the vicinity of the vehicle (regardless of theirpriority) with at least a minimum frequency (e.g., once per second).

The prediction data 220 generated for the high-priority agents 224 bythe high-priority prediction model 226, and any prediction data 220generated for the low-priority agents by the low-priority predictionmodel 228, is provided to the planning system 110 for use in generatingplanning decisions.

FIG. 3 is a block diagram of an example data representation system 208.The data representation system 208 is an example of a system implementedas computer programs on one or more computers in one or more locationsin which the systems, components, and techniques described below areimplemented.

The data representation system 208 processes the historical data 202 togenerate the trajectory representation data 210. The trajectoryrepresentation data 210 is composed of multiple “channels”. Each channelis a two-dimensional (2D) array of data values that represents a“top-down” perspective of the environment in the vicinity of thevehicle. Each position in each channel corresponds to a respectivespatial position in the environment and can be indexed by respectivecoordinates. Each of the channels have the same dimensionality (i.e.,the same number of rows and columns), the same top-down perspective ofthe environment, and are aligned (i.e., registered) with one another.That is, positions which are indexed by the same coordinates indifferent channels correspond to the same spatial position in theenvironment. In other words, corresponding positions in differentchannels correspond to the same spatial position in the environment.

To represent the trajectory of the vehicle, the trajectoryrepresentation data 210 includes a vehicle time channel and respectivevehicle motion parameter channels corresponding to each of apredetermined number of motion parameters. Each of the motion parameterscharacterizes a respective characteristic of the motion of the vehicle,for example, the velocity, acceleration, or heading of the vehicle. Asdepicted in FIG. 3, the trajectory representation data 210 may include avehicle time channel 302, a vehicle velocity channel 304, a vehicleacceleration channel 306, and a vehicle heading channel 308.

The vehicle time channel and the vehicle motion parameter channelsrepresent the previous trajectory of the vehicle up to the current timepoint, and optionally, a candidate future trajectory of the vehicleafter the current time point. A candidate future trajectory of thevehicle refers to a possible trajectory of the vehicle after the currenttime point. More specifically, a candidate future trajectory of thevehicle specifies, for each of multiple future time points after thecurrent time point, a spatial position in the environment that can beoccupied by the agent at the future time point. For each of the multiplefuture time points, the candidate future trajectory further specifiespossible values of each of the predetermined number of motion parametersthat characterize the motion of the vehicle at the future time point.

For brevity, the description which follows refers to the vehicle timechannel and the vehicle motion parameter channels representing theprevious trajectory of the vehicle up to the current time point. Itshould be understood that the vehicle time channel and the vehiclemotion parameter channels can similarly represent a candidate futuretrajectory of the vehicle after the current time point in addition tothe previous trajectory of the vehicle up to the current time point.

The vehicle time channel represents the respective time points at whichthe vehicle occupies different spatial positions in the environment inthe previous trajectory of the vehicle. Each motion parameter channelrepresents the values of the respective motion parameter characterizingthe motion of the vehicle when the vehicle occupies different spatialpositions in the environment in the previous trajectory of the vehicle.In particular, for each spatial position in the environment which isoccupied by the vehicle, the data value in the vehicle time channelwhich corresponds to the spatial position defines the time point atwhich the vehicle occupies the spatial position. Moreover, the datavalue in each respective vehicle motion parameter channel whichcorresponds to the spatial position defines the value of the respectivemotion parameter characterizing the motion of the vehicle when thevehicle occupies the spatial position in the environment.

Generally, the environment may include multiple spatial positions whichare not included in either the previous trajectory or the candidatefuture trajectory of the vehicle. For these spatial positions, the datarepresentation system 208 can set the data values in the vehicle timechannel and the vehicle motion parameter channels which correspond tothese spatial positions to a default value (e.g., the value 0).

When the same spatial position in the environment is occupied by thevehicle at multiple time points, then the system 208 can set therespective data values in the vehicle time channel and motion parameterchannels which correspond to the spatial position to any appropriatevalues. For example, the system 208 can set the respective data valuesin the vehicle time channel and motion parameter channels whichcorrespond to the spatial position in accordance with the last timepoint when the vehicle occupies the spatial position. That is, thesystem 208 can set the data value in the vehicle time channel whichcorresponds to the spatial position to define the last time point whenthe vehicle occupies the spatial position. Moreover, the system 208 canset the respective data values in the vehicle motion parameter channelsto define the values of the respective motion parameters characterizingthe motion of the vehicle when the vehicle last occupies the spatialposition.

To represent the trajectories of the agents in the environment in thevicinity of the vehicle, the trajectory representation data optionallyincludes an auxiliary time channel and respective auxiliary motionparameter channels corresponding to each of the predetermined number ofmotion parameters. As depicted in FIG. 3, the trajectory representationdata 210 may include an auxiliary time channel 310, an auxiliaryvelocity channel 312, an auxiliary acceleration channel 314, and anauxiliary heading channel 316.

The auxiliary time channel and the auxiliary motion parameter channelsjointly represent the previous trajectories of the agents up to thecurrent time point, and optionally, predicted future trajectories of theagents after the current time point. The system 208 may obtain thepredicted future trajectories of the agents as behavior predictionoutputs of a behavior prediction neural network from a previous timepoint. A predicted future trajectory of an agent specifies, for each ofmultiple future time points after the current time point, a spatialposition in the environment that can be occupied by the agent at thefuture time point. For each of the multiple future time points, thepredicted future trajectory further specifies possible values of each ofthe predetermined number of motion parameters that characterize themotion of the agent at the future time point.

For brevity, the description which follows refers to the auxiliary timechannel and the auxiliary motion parameter channels representing theprevious trajectories of the agents up to the current time point. Itshould be understood that the auxiliary time channel and the auxiliarymotion parameter channels can similarly represent predicted futuretrajectories of the agents after the current time point in addition tothe previous trajectories of the agents up to the current time point.

The auxiliary time channel jointly represents the respective time pointsat which the agents occupy different spatial positions in theenvironment in the previous trajectories of the agents. Each auxiliarymotion parameter channel represents the values of the respective motionparameters characterizing the motion of the agents when the agentsoccupy different spatial positions in the environment in the previoustrajectories of the agents. In particular, for each spatial position inthe environment which is occupied by one of the agents, the data valuein the auxiliary time channel which corresponds to the spatial positiondefines the time point at which the agent occupies the spatial position.Moreover, the data value in each respective auxiliary motion parameterchannel which corresponds to the spatial position defines the value ofthe respective motion parameter characterizing the motion of the agentwhen the agent occupies the spatial position in the environment.

Generally, the environment may include multiple spatial positions whichare not included in either the previous trajectory or the predictedfuture trajectory of any of the agents. For these spatial positions, thedata representation system 208 can set the data values in the auxiliarytime channel and the auxiliary motion parameter channels whichcorrespond to these spatial positions to a default value (e.g., thevalue 0).

When the same spatial position in the environment is occupied by agentsat multiple time points, then the system 208 can set the respective datavalues in the auxiliary time channel and auxiliary motion parameterchannels which correspond to the spatial position to any appropriatevalues. For example, the system 208 can set the respective data valuesin the auxiliary time channel and auxiliary motion parameter channelswhich correspond to the spatial position in accordance with the lasttime point when one of the agents occupies the spatial position.

By jointly representing the trajectories of the agents using a singleauxiliary time channel and a single auxiliary motion parametercorresponding to each motion parameter, the system 208 can generatetrajectory representation data with a predetermined dimensionalityirrespective of the (variable) number of agents. In this manner, thetrajectory representation data 210 generated by the system 110 can bereadily processed by the importance scoring model, which is configuredto process trajectory representation data 210 of the predetermineddimensionality.

In some implementations, the system 208 can include further channels inthe trajectory representation data 210 in addition to the time channelsand motion parameter channels. For example, the trajectoryrepresentation data 210 can include one or more of: a road-graphchannel, a vehicle localization channel, and an auxiliary localizationchannel. A road-graph channel represents a known geometry of theenvironment in the vicinity of the vehicle 102. For example, theroad-graph channel may represent the positions of different features ofthe environment, including: the road, different lanes in the road,crosswalks, traffic lights, construction zones, school zones, and thelike. A vehicle localization channel represents the spatial position ofthe vehicle in the environment at the current time point (e.g., asdefined by a bounding box). An auxiliary localization channel (e.g., theauxiliary localization channel 318) jointly represents the positions ofeach of the agents in the environment at the current time point (e.g.,as defined by bounding boxes). In the example depicted in FIG. 3, theroad-graph channel and the vehicle localization channel are superimposedonto a single channel 320.

The system 110 determines the trajectory representation data 210 byaligning and channel-wise concatenating the generated channels, asdepicted by 322. That is, the trajectory representation data 210 is aconcatenation of the generated channels. By implicitly representing therespective trajectories of the vehicle and the agents in this format,the system 208 generates a representation which is both compact and canbe effectively processed by the importance scoring model. In particular,the importance scoring model may be a convolutional neural networkmodel. The importance scoring model can process the trajectoryrepresentation data using convolutional neural network layers defined bymulti-dimensional (e.g., two- or three-dimensional) convolutionalfilters, thereby enabling the importance scoring model to learn complexspatial relationships between different spatial regions of theenvironment.

FIG. 4 is an illustration of an example process by which the datarepresentation system 208 can generate a vehicle time channel 402, avehicle velocity channel 404, and a vehicle heading channel 406, whichrepresent a previous trajectory of the vehicle up to the current timepoint and a candidate future trajectory of the vehicle after the currenttime point.

The data which defines the previous trajectory of the vehicle (e.g., asobtained by the data representation system 208 from historical data 202)and the candidate future trajectory of the vehicle is represented in atabular format 408. Each row of the table defines a time point, aspatial position the vehicle occupies in the environment at the timepoint, a velocity of the vehicle at the time point, and a heading of thevehicle at the time point.

For example, the first row of the table 408 defines that at time point−3 (e.g., 3 seconds before the current time point), the spatial positionoccupied by the vehicle in the environment is defined by the coordinates[−3, −2] in the channel frame of reference, the velocity of the vehicleis 45 mph, and the heading of the vehicle is 45 degrees (e.g., clockwisefrom North). The coordinates [−3, −2] are expressed in the channel frameof reference and can be mapped to express a spatial position in anenvironment frame of reference. For example, the coordinates in thechannel frame of reference may represent 5 foot increments in aNorth-South-East-West environment frame of reference which is centeredon the vehicle. In this example, the coordinates [−3, −2] in the channelframe of reference may represent a spatial position in the environmentwhich is 15 feet West and 10 feet South of the spatial position occupiedby the vehicle at the current time point. As another example, the lastrow of the table 408 defines that at time point +2 (e.g., 2 secondsafter the current time point), the spatial position the vehicle occupies(i.e., according to the candidate future trajectory) is defined by thecoordinates [2,0] in the channel frame of reference, the velocity of thevehicle is 49 mph, and the heading of the vehicle is 90 degrees.

The data representation system 208 sets the data values in the vehicletime channel corresponding to spatial positions [−3, −2], [−2, −1], [−1,0], [0, 0],

1,

],

nd

2,

] to the respective time points −3, −2, −1, 0,

1,

nd

2 at which the vehicle occupies the respective spatial positions. Forclarity, the data values in the vehicle time channel corresponding tothe other spatial positions are shown as blank. Generally, the datarepresentation system 208 sets the data values in the vehicle timechannel corresponding to the other spatial positions to a default value(e.g., the value 0). Similarly, the data representation system 208 setsthe data values in the vehicle velocity channel corresponding to spatialpositions [−3, −2], [−2, −1], [−1, 0], [0, 0],

1,

0],

nd

2,

]

o the respective velocity values 45, 47, 51, 49,

9,

nd

9 which define the velocity (in mph) of the vehicle when the vehicleoccupies the respective spatial positions. Similarly, the datarepresentation system 208 sets the data values in the vehicle headingchannel corresponding to spatial positions [−3, −2], [−2, −1], [−1, 0],[0, 0],

1,

],

nd

2,

] to the respective heading values 45, 45, 90, 90, 90, and 90 whichdefine the heading (in degrees) of the vehicle when the vehicle occupiesthe respective spatial positions.

In some implementations, the data representation system 208 determinesthe channel frame of reference to cause the spatial position occupied bythe vehicle at the current time point to correspond to the data value inthe “center” of each of the channels. Generating trajectoryrepresentation data with a consistent channel frame of reference canfacilitate training of the importance scoring model on the trajectoryrepresentation data.

FIG. 5 is a flow diagram of an example process 500 for generatingprediction data to be provided to a planning system. For convenience,the process 500 will be described as being performed by a system of oneor more computers located in one or more locations. For example, anon-board system, e.g., the on-board system 100 of FIG. 1, appropriatelyprogrammed in accordance with this specification, can perform theprocess 500.

The system generates trajectory representation data that represents therepresents the trajectory of the vehicle (502). Optionally, thetrajectory representation data may further include one or more of: (i) ajoint representation of the trajectories of the agents in theenvironment in the vicinity of the vehicle, (ii) a road-graph channelthat represents the known geometry of the environment in the vicinity ofthe vehicle, (iii) a vehicle localization channel that represents thespatial position of the vehicle in the environment at the current timepoint, and (iv) an auxiliary localization channel that represents thepositions of each of the agents in the environment at the current timepoint. An example data representation system for generating thetrajectory representation data is described with reference to FIG. 3.

The system generates a respective importance score for each agent in thevicinity of the vehicle by processing the trajectory representation datausing an importance scoring model (504). The importance scoring modelcan be implemented as any appropriate prediction model, for example, asa neural network, a random forest, or support vector machine. In aparticular example, the importance scoring model may be a convolutionalneural network, that is, a neural network that includes one or moreconvolutional layers. The convolutional neural network may be configuredto generate an output channel that is represented as a two-dimensionalarray of data values, where each position in the output channelcorresponds to a respective spatial position in the environment. Foreach spatial position in the environment that is occupied by an agent,the position in the output channel that corresponds to the spatialposition defines the importance score of the agent. In this example, thesystem may determine the importance scores for each agent as the valuedefined by the position in the output channel that corresponds to thespatial position in the environment that is occupied by the agent.

Optionally, the system refines the importance scores for the agentsusing an importance score refining model (506). More specifically, thesystem generates a respective feature representation of each agent inthe vicinity of the vehicle based in part on the output channelgenerated by the importance scoring model. Thereafter, the systemprocesses the feature representation of each agent using the importancescore refining model to generate a “refined” importance score for eachagent which may be more accurate than the importance score generated bythe initial importance scoring model. The importance score refiningmodel can be any appropriate machine learning model, for example, arandom forest model, a gradient boosted decision tree model, a neuralnetwork model, or a linear model. The importance score refining modelcan be trained in a similar manner as the importance scoring model, asdescribed with reference to FIG. 1. In a particular example, the lossfunction may be a cross-entropy or logistic loss function thatcharacterizes whether the ranking of pairs of agents defined by therefined importance scores are consistent with the ranking of the pairsof agents defined by the labels in the training examples. In particular,the importance score refining model can be trained by sampling pairs ofagents, determining respective importance scores for each agent, andadjusting the importance score refining model parameters based onwhether the respective importance scores for each of the agents isconsistent with the ranking of the pair of agents defined by the labelof a corresponding training example.

To generate the feature representation of an agent, the system mayextract one or more “importance score features” from the output channelgenerated by the importance scoring model. In particular the system mayextract statistics (e.g., the maximum and the average) of the values inregions of the output channel of various sizes around the position inthe output channel that corresponds to the spatial location of the agentin the environment. For each agent, the system may also generate one ormore “additional features” based on the sensor data captured by thesensors of the vehicle. For example, for each agent, the additionalfeatures may include: (1) the distance of the agent from the vehicle,(2) whether the agent is in front of the vehicle, (3) the current speedof the agent, (4) the current acceleration of the agent, (5) a type ofthe agent (e.g., cyclist, car, pedestrian, or child), (6) the distanceof the agent from a candidate future trajectory of the vehicle, (7) anamount of time until the candidate future trajectory of the vehicle isclosest to the agent, (8) an amount of time until the predicted futuretrajectory of the agent intersects the candidate future trajectory ofthe vehicle, and (9) the minimum time for the agent to collide with thevehicle if no action is taken. The system may determine the featurerepresentation of each agent by combining (e.g., concatenating) theimportance score features and the additional features for the agent.

In some cases, the importance scoring model may generate an output thatdefines importance scores for agents located within a spatial regionaround the vehicle (e.g., a square region centered on the vehicle)without defining importance score for agents located outside the spatialregion. For example, the importance scoring model may be acomputationally intensive neural network model which generates an outputthat only defines importance scores for agents located within thespatial region around the vehicle for reasons of computationalefficiency. However, for an agent outside the spatial region around thevehicle, the system may nonetheless generate a feature representationfor the agent based on the additional features derived from the sensordata generated by the vehicle (as described above). For the componentsof the feature representation corresponding to the importance scorefeatures (as described above), the feature representation may includedefault values or values understood to indicate that the importancescore features are missing (e.g., “NaN” values). The system may processfeature representations of agents outside the spatial region around thevehicle using the importance score refining model to generate importancescores for the agents.

In general, the refined importance scores generated by the importancescore refining model may be more accurate than the importance scoresgenerated by the importance scoring model. In particular, the importancescore refining model can integrate hand-designed features characterizingthe agents in the vicinity of the vehicle (e.g., which indicate thetypes of the agents) with importance score features that cancharacterize interactions between the various agents.

The system identifies the high-priority agents in the vicinity of thevehicle based on the importance scores (508). For example, the systemmay identify each agent with an importance score that satisfies apredetermined threshold as a high-priority agent. As another example,the system may identify a predetermined number of the agents with thehighest importance scores as high-priority agents. In certainsituations, the system may identify none or all of the agents in thevicinity of the vehicle as high-priority agents.

The system generates prediction data for the high-priority agents usinga prediction model (510). In some implementations, the prediction modelmay generate classification prediction data which predicts the type ofan agent (e.g., animal, pedestrian pushing cart, pedestrian directingtraffic, pedestrian riding scooter, car, truck, and the like). In someimplementations, the behavior prediction model may generate behaviorprediction data which characterizes a predicted future behavior of anagent (e.g., braking, accelerating, changing lanes, and the like). Inthese implementations, the behavior prediction model may generatebehavior prediction data for an agent by, for example, processing arepresentation of the trajectory of the agent up to the current timepoint using a behavior prediction neural network. A few examples follow.

In some implementations, the behavior prediction data for an agentdefines, for each of multiple spatial locations in the environment, arespective probability that the agent will occupy the spatial locationat a specified time point after the current time point. In theseimplementations, the output layer of the behavior prediction neuralnetwork may be a sigmoid layer with a respective neuron corresponding toeach of the spatial locations in the environment. The probability thatthe agent will occupy a particular spatial location at the specifiedtime point after the current time point may be defined as the activationof the neuron in the sigmoid output layer that corresponds to theparticular spatial location.

In some implementations, the behavior prediction data for an agentdefines a probability that a candidate future trajectory of the agent isthe actual future trajectory of the agent. In these implementations, theoutput layer of the behavior prediction neural network may include asingle neuron, where the activation of the neuron is defined as theoutput of an activation function with an output range of [0, 1] (e.g., asigmoid activation function). The probability that the candidate futuretrajectory of the agent is the actual future trajectory of the agent maybe defined as the activation of the single neuron in the output layer.

In some implementations, the behavior prediction data for an agentdefines a respective probability that the agent will make each of apredetermined number of possible driving decisions. For example, thepossible driving decisions may include one or more of: yielding,changing lanes, passing, braking, and accelerating. In theseimplementations, the output layer of the behavior prediction neuralnetwork may be a sigmoid layer with a respective neuron corresponding toeach of the possible driving decisions. The probability that the agentwill make a particular driving decision after the current time point maybe defined as the activation of the neuron in the sigmoid output layerthat corresponds to the particular driving decision.

Optionally, the system generates prediction data for any low-priorityagents (i.e., agents that are not designated as high-priority agents)using one or more prediction models which are less computationallyintensive than the prediction model used to generate the prediction datafor the high-priority agents (512). For example, the prediction model(s)used to generate prediction data for the low-priority agents may havefewer model parameters than the prediction model used to generateprediction data for the high-priority agents. In a particular example,the prediction models may be neural networks, and the neural network(s)used for the low-priority agents may have fewer neural network weightsthan the neural network(s) used for the high-priority agents. In somecases, the system may determine not to generate any prediction data forsome or all of the low-priority agents (e.g., if their respectiveimportance scores do not satisfy a predetermined threshold).

The system provides the generated prediction data (for the high-priorityagents, and optionally, for any low-priority agents) to the planningsystem of the vehicle (514). The planning system uses the predictiondata to generate planning decisions which plan the future trajectory ofthe vehicle.

FIG. 6 is a flow diagram of an example process 600 for generating atraining example which can be used to train an importance scoring model.For convenience, the process 600 will be described as being performed bya system of one or more computers located in one or more locations. Forexample, a training system, e.g., the training system 120 of FIG. 1,appropriately programmed in accordance with this specification, canperform the process 600.

The system obtains sensor data characterizing the environment in avicinity of a vehicle at a given time point (602). The system may obtainthe sensor data from a sensor data log which is stored in a physicaldata storage device or a logical data storage area. The sensor data maybe real sensor data characterizing a real-world environment in thevicinity of a vehicle, or simulated sensor data characterizing asimulated environment in the vicinity of a simulated vehicle. Asdescribed with reference to FIG. 1, the sensor data may be generated byone or more sensors of the vehicle, including one or more of: lasersensors, radar sensors, and camera sensors.

The system generates respective prediction data for the agents in thevicinity of the vehicle (604). For example, the system may generaterespective prediction data for every agent in the vicinity of thevehicle which is identified by an object detection system of thevehicle. The behavior prediction data generated by the system for eachagent characterizes the predicted future behavior of the agent. Forexample, for each of the agents in the vicinity of the vehicle, thebehavior prediction data may define respective probabilities that theagent makes each of a predetermined number of possible driving decisions(e.g., yielding, changing lanes, passing, braking, or accelerating). Togenerate the behavior prediction data for an agent, the system mayprocess a representation of the trajectory of the agent up to the giventime point using a behavior prediction model.

The system provides the behavior prediction data to a planning systemwhich is configured to process the behavior prediction data to generateplanning decisions which plan a future trajectory for the vehicle (606).The planning decisions generated by the planning system can, forexample, include: yielding (e.g., to other vehicles), stopping (e.g., ata Stop sign), passing other vehicles, adjusting vehicle lane position toaccommodate a bicyclist, slowing down in a school or construction zone,merging (e.g., onto a highway), and parking.

The system processes the planning decisions generated by the planningsystem to determine a ranking of the agents in the vicinity of thevehicle at the given time point in order of their impact on the planningdecisions (608). The system may determine the ranking of the agentsbased on how much the behavior of each agent prompts the planning systemto generate planning decisions which would change the future trajectoryof the vehicle. For example, the system may determine a score for eachagent based on how much each agent prompts the planning system togenerate planning decisions which would change the future trajectory ofthe vehicle, and then determine the ranking of the agents using thescores. In a particular example, the system may determine a score of 12for Agent A, a score of 0 for Agent B, and a score of 4.5 for Agent C,in which case the system may determine the ranking of the agents as:[A,C,B].

For example, each of the planning decisions may define: (i) an action tobe performed by the vehicle (e.g., accelerating, decelerating, stopping,or swerving), and (ii) an agent in the vicinity of the vehicle whichprompts the planning system to generate the planning decision (ifapplicable). In this example, the system may generate a score of 0 foragents which do not prompt the planning system to generate any planningdecisions. For an agent which does prompt the planning system togenerate a planning decision, the system may determine the score for theagent as a predetermined function of the action specified by theplanning decision. For example, if the planning decision specifies theaction of braking at 10 feet per second squared, the system maydetermine the score for the agent to be 10. If a single agent promptsthe planning system to generate multiple planning decisions (e.g.,braking and swerving), the system can determine the score for the agentas a sum (or other combination) of the respective scores generated foreach of the multiple planning decisions.

The ranking of the agents can be broadly understood to be any data whichdefines that certain agents in the vicinity of the vehicle have agreater impact on the planning decisions than certain other agents inthe vicinity of the vehicle. For example, the ranking of the agents maydefine an explicit ordering of the agents from highest-rank tolowest-ranked, where each agent is assigned a distinct rank. As anotherexample, the ranking of the agents may define a partition of the agentsinto multiple groups, where each group includes one or more agents. Foreach pair of groups including a first group and a second group, theranking may define whether the agents in the first group have a greaterimpact on the planning decisions than the agents in the second group.The agents within a given group may be understood to have an equivalentimpact on the planning decisions.

The system generates a training example which includes: (i) an input ofthe training importance scoring model that includes data characterizingthe trajectory of the vehicle at a respective time point, and (ii) labeldata defining the ranking of the agents in the vicinity of the vehicle(610). As described with reference to FIG. 3, the system can generatethe input of the training importance scoring model that is included inthe training example using a data representation system.

This specification uses the term “configured” in connection with systemsand computer program components. For a system of one or more computersto be configured to perform particular operations or actions means thatthe system has installed on it software, firmware, hardware, or acombination of them that in operation cause the system to perform theoperations or actions. For one or more computer programs to beconfigured to perform particular operations or actions means that theone or more programs include instructions that, when executed by dataprocessing apparatus, cause the apparatus to perform the operations oractions.

Embodiments of the subject matter and the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, in tangibly-embodied computer software or firmware, incomputer hardware, including the structures disclosed in thisspecification and their structural equivalents, or in combinations ofone or more of them. Embodiments of the subject matter described in thisspecification can be implemented as one or more computer programs, i.e.,one or more modules of computer program instructions encoded on atangible non-transitory storage medium for execution by, or to controlthe operation of, data processing apparatus. The computer storage mediumcan be a machine-readable storage device, a machine-readable storagesubstrate, a random or serial access memory device, or a combination ofone or more of them. Alternatively or in addition, the programinstructions can be encoded on an artificially-generated propagatedsignal, e.g., a machine-generated electrical, optical, orelectromagnetic signal, that is generated to encode information fortransmission to suitable receiver apparatus for execution by a dataprocessing apparatus.

The term “data processing apparatus” refers to data processing hardwareand encompasses all kinds of apparatus, devices, and machines forprocessing data, including by way of example a programmable processor, acomputer, or multiple processors or computers. The apparatus can alsobe, or further include, special purpose logic circuitry, e.g., an FPGA(field programmable gate array) or an ASIC (application-specificintegrated circuit). The apparatus can optionally include, in additionto hardware, code that creates an execution environment for computerprograms, e.g., code that constitutes processor firmware, a protocolstack, a database management system, an operating system, or acombination of one or more of them.

A computer program, which may also be referred to or described as aprogram, software, a software application, an app, a module, a softwaremodule, a script, or code, can be written in any form of programminglanguage, including compiled or interpreted languages, or declarative orprocedural languages; and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A program may, but neednot, correspond to a file in a file system. A program can be stored in aportion of a file that holds other programs or data, e.g., one or morescripts stored in a markup language document, in a single file dedicatedto the program in question, or in multiple coordinated files, e.g.,files that store one or more modules, sub-programs, or portions of code.A computer program can be deployed to be executed on one computer or onmultiple computers that are located at one site or distributed acrossmultiple sites and interconnected by a data communication network.

In this specification the term “engine” is used broadly to refer to asoftware-based system, subsystem, or process that is programmed toperform one or more specific functions. Generally, an engine will beimplemented as one or more software modules or components, installed onone or more computers in one or more locations. In some cases, one ormore computers will be dedicated to a particular engine; in other cases,multiple engines can be installed and running on the same computer orcomputers.

The processes and logic flows described in this specification can beperformed by one or more programmable computers executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby special purpose logic circuitry, e.g., an FPGA or an ASIC, or by acombination of special purpose logic circuitry and one or moreprogrammed computers.

Computers suitable for the execution of a computer program can be basedon general or special purpose microprocessors or both, or any other kindof central processing unit. Generally, a central processing unit willreceive instructions and data from a read-only memory or a random accessmemory or both. The essential elements of a computer are a centralprocessing unit for performing or executing instructions and one or morememory devices for storing instructions and data. The central processingunit and the memory can be supplemented by, or incorporated in, specialpurpose logic circuitry. Generally, a computer will also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto-optical disks, or optical disks. However, a computer need nothave such devices. Moreover, a computer can be embedded in anotherdevice, e.g., a mobile telephone, a personal digital assistant (PDA), amobile audio or video player, a game console, a Global PositioningSystem (GPS) receiver, or a portable storage device, e.g., a universalserial bus (USB) flash drive, to name just a few.

Computer-readable media suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks,e.g., internal hard disks or removable disks; magneto-optical disks; andCD-ROM and DVD-ROM disks.

To provide for interaction with a user, embodiments of the subjectmatter described in this specification can be implemented on a computerhaving a display device, e.g., a CRT (cathode ray tube) or LCD (liquidcrystal display) monitor, for displaying information to the user and akeyboard and a pointing device, e.g., a mouse or a trackball, by whichthe user can provide input to the computer. Other kinds of devices canbe used to provide for interaction with a user as well; for example,feedback provided to the user can be any form of sensory feedback, e.g.,visual feedback, auditory feedback, or tactile feedback; and input fromthe user can be received in any form, including acoustic, speech, ortactile input. In addition, a computer can interact with a user bysending documents to and receiving documents from a device that is usedby the user; for example, by sending web pages to a web browser on auser's device in response to requests received from the web browser.Also, a computer can interact with a user by sending text messages orother forms of message to a personal device, e.g., a smartphone that isrunning a messaging application, and receiving responsive messages fromthe user in return.

Data processing apparatus for implementing machine learning models canalso include, for example, special-purpose hardware accelerator unitsfor processing common and compute-intensive parts of machine learningtraining or production, i.e., inference, workloads.

Machine learning models can be implemented and deployed using a machinelearning framework, e.g., a TensorFlow framework, a Microsoft CognitiveToolkit framework, an Apache Singa framework, or an Apache MXNetframework.

Embodiments of the subject matter described in this specification can beimplemented in a computing system that includes a back-end component,e.g., as a data server, or that includes a middleware component, e.g.,an application server, or that includes a front-end component, e.g., aclient computer having a graphical user interface, a web browser, or anapp through which a user can interact with an implementation of thesubject matter described in this specification, or any combination ofone or more such back-end, middleware, or front-end components. Thecomponents of the system can be interconnected by any form or medium ofdigital data communication, e.g., a communication network. Examples ofcommunication networks include a local area network (LAN) and a widearea network (WAN), e.g., the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other. In someembodiments, a server transmits data, e.g., an HTML page, to a userdevice, e.g., for purposes of displaying data to and receiving userinput from a user interacting with the device, which acts as a client.Data generated at the user device, e.g., a result of the userinteraction, can be received at the server from the device.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinvention or on the scope of what may be claimed, but rather asdescriptions of features that may be specific to particular embodimentsof particular inventions. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially be claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings and recited inthe claims in a particular order, this should not be understood asrequiring that such operations be performed in the particular ordershown or in sequential order, or that all illustrated operations beperformed, to achieve desirable results. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system modules and components in the embodimentsdescribed above should not be understood as requiring such separation inall embodiments, and it should be understood that the described programcomponents and systems can generally be integrated together in a singlesoftware product or packaged into multiple software products.

Particular embodiments of the subject matter have been described. Otherembodiments are within the scope of the following claims. For example,the actions recited in the claims can be performed in a different orderand still achieve desirable results. As one example, the processesdepicted in the accompanying figures do not necessarily require theparticular order shown, or sequential order, to achieve desirableresults. In some cases, multitasking and parallel processing may beadvantageous.

What is claimed is:
 1. A method performed by one or more data processingapparatus, the method comprising: processing an input that characterizesa trajectory of a vehicle in an environment using an importance scoringmodel to generate an output that defines a respective importance scorefor each of a plurality of agents in the environment in the vicinity ofthe vehicle, wherein the importance score for an agent characterizes anestimated impact of the agent on planning decisions generated by aplanning system of the vehicle which plans a future trajectory of thevehicle; identifying, as high-priority agents, a proper subset of theplurality of agents with the highest importance scores; for only thoseagents of the plurality of agents that are identified as high-priorityagents, generating data characterizing the agents using a firstprediction model; and providing the data characterizing thehigh-priority agents generated using the first prediction model to theplanning system of the vehicle to generate the planning decisions whichplan the future trajectory of the vehicle.
 2. The method of claim 1,further comprising: obtaining historical data characterizing thetrajectory of the vehicle in the environment, the historical datacomprising, for each of a plurality of previous time points, datadefining: (i) a spatial position in the environment occupied by thevehicle at the previous time point, and (ii) respective values of eachmotion parameter in a predetermined set of motion parameters, whereinthe value of each motion parameter characterizes a respective feature ofa motion of the vehicle at the previous time point; generating arepresentation of the trajectory of the vehicle in the environment,wherein: the representation of the trajectory of the vehicle in theenvironment is a concatenation of a plurality of channels; each channelis represented as a two-dimensional array of data values; each positionin each channel corresponds to a respective spatial position in theenvironment; corresponding positions in different channels correspond tothe same spatial position in the environment; the channels comprise atime channel and a respective motion channel corresponding to eachmotion parameter in the predetermined set of motion parameters; and foreach particular spatial position in the environment occupied by thevehicle at a particular previous time point: the position in the timechannel which corresponds to the particular spatial position defines theparticular previous time point; and for each motion channel, theposition in the motion channel which corresponds to the particularspatial position defines the value of the motion parameter correspondingto the motion channel at the particular previous time point; whereinprocessing an input that characterizes a trajectory of the vehicle inthe environment comprises processing an input that includes therepresentation of the trajectory of the vehicle in the environment. 3.The method of claim 2, wherein: the output of the importance scoringmodel comprises an output channel that is represented as atwo-dimensional array of data values; each position in the outputchannel corresponds to a respective spatial position in the environment;and for each spatial position in the environment that is occupied by anagent of the plurality of agents at a current time point, the positionin the output channel that corresponds to the spatial position definesan importance score of the agent.
 4. The method of claim 3, furthercomprising, for each agent of the plurality of agents: generating arespective feature representation of the agent, comprising: generatingone or more importance score features of the agent from the outputchannel; generating one or more additional features of the agent basedon sensor data captured by one or more sensors of the vehicle; andgenerating the feature representation of the agent from the importancescore features of the agent and the additional features of the agent;processing the feature representation of the agent using an importancescore refining model to generate a refined importance score for theagent that characterizes an estimated impact of the agent on planningdecisions generated by a planning system of the vehicle which plans afuture trajectory of the vehicle.
 5. The method of claim 2, whereinobtaining the respective values of each motion parameter in thepredetermined set of motion parameters for a previous time pointcomprises one or more of: obtaining the value of a velocity motionparameter which characterizes a velocity of the vehicle at the previoustime point; obtaining the value of an acceleration motion parameterwhich characterizes an acceleration of the vehicle at the previous timepoint; and obtaining the value of a heading motion parameter whichcharacterizes a heading of the vehicle at the previous time point. 6.The method of claim 2, wherein the input processed by the importancescoring model further comprises one or more of: (i) a road-graph channelrepresenting a known geometry of the environment, (ii) a vehiclelocalization channel which represents a spatial position of the vehiclein the environment at a current time point by a vehicle bounding box,and (iii) an auxiliary localization channel which represents respectivespatial positions of the plurality of agents in the environment at acurrent time point by respective bounding boxes.
 7. The method of claim2, further comprising generating a joint representation of trajectoriesof the plurality of agents in the environment in the vicinity of thevehicle, wherein the input processed by the importance scoring modelfurther comprises the joint representation of the trajectories of theplurality of agents.
 8. The method of claim 7, wherein: the jointrepresentation of the trajectories of the plurality of agents in theenvironment comprises an auxiliary time channel and a respectiveauxiliary motion channel corresponding to each motion parameter in thepredetermined set of motion parameters; each channel is represented as atwo-dimensional array of data values and each data value in each channelcorresponds to a respective spatial position in the environment; and foreach particular spatial position in the environment occupied by aparticular agent of the plurality of agents at a particular previoustime point: the data value in the auxiliary time channel whichcorresponds to the particular spatial position defines the particularprevious time point; and for each auxiliary motion channel, the datavalue in the auxiliary motion channel which corresponds to theparticular spatial position defines a value of the motion parametercorresponding to the auxiliary motion channel which characterizes arespective feature of a motion of the particular agent at the particularprevious time point.
 9. The method of claim 1, wherein identifying, ashigh-priority agents, a proper subset of the plurality of agents withthe highest importance scores comprises: identifying, as high-priorityagents, a predetermined number of the plurality of agents with thehighest importance scores.
 10. The method of claim 1, furthercomprising: for one or more of the plurality of agents that are notidentified as high-priority agents, generating data characterizing theone or more agents using a second prediction model, wherein the firstprediction model has a first number of model parameters, the secondprediction model has a second number of model parameters, and the firstnumber of model parameters is greater than the second number of modelparameters; and providing the data characterizing the one or more agentsgenerated using the second prediction model to the planning system inaddition to the data characterizing the high priority agents generatedusing the first prediction model.
 11. A system comprising: one or morecomputers; and one or more storage devices communicatively coupled tothe one or more computers, wherein the one or more storage devices storeinstructions that, when executed by the one or more computers, cause theone or more computers to perform operations comprising: processing aninput that characterizes a trajectory of a vehicle in an environmentusing an importance scoring model to generate an output that defines arespective importance score for each of a plurality of agents in theenvironment in the vicinity of the vehicle, wherein the importance scorefor an agent characterizes an estimated impact of the agent on planningdecisions generated by a planning system of the vehicle which plans afuture trajectory of the vehicle; identifying, as high-priority agents,a proper subset of the plurality of agents with the highest importancescores; for only those agents of the plurality of agents that areidentified as high-priority agents, generating data characterizing theagents using a first prediction model; and providing the datacharacterizing the high-priority agents generated using the firstprediction model to the planning system of the vehicle to generate theplanning decisions which plan the future trajectory of the vehicle. 12.The system of claim 11, wherein the operations further comprise:obtaining historical data characterizing the trajectory of the vehiclein the environment, the historical data comprising, for each of aplurality of previous time points, data defining: (i) a spatial positionin the environment occupied by the vehicle at the previous time point,and (ii) respective values of each motion parameter in a predeterminedset of motion parameters, wherein the value of each motion parametercharacterizes a respective feature of a motion of the vehicle at theprevious time point; generating a representation of the trajectory ofthe vehicle in the environment, wherein: the representation of thetrajectory of the vehicle in the environment is a concatenation of aplurality of channels; each channel is represented as a two-dimensionalarray of data values; each position in each channel corresponds to arespective spatial position in the environment; corresponding positionsin different channels correspond to the same spatial position in theenvironment; the channels comprise a time channel and a respectivemotion channel corresponding to each motion parameter in thepredetermined set of motion parameters; and for each particular spatialposition in the environment occupied by the vehicle at a particularprevious time point: the position in the time channel which correspondsto the particular spatial position defines the particular previous timepoint; and for each motion channel, the position in the motion channelwhich corresponds to the particular spatial position defines the valueof the motion parameter corresponding to the motion channel at theparticular previous time point; wherein processing an input thatcharacterizes a trajectory of the vehicle in the environment comprisesprocessing an input that includes the representation of the trajectoryof the vehicle in the environment.
 13. The system of claim 12, wherein:the output of the importance scoring model comprises an output channelthat is represented as a two-dimensional array of data values; eachposition in the output channel corresponds to a respective spatialposition in the environment; and for each spatial position in theenvironment that is occupied by an agent of the plurality of agents at acurrent time point, the position in the output channel that correspondsto the spatial position defines an importance score of the agent. 14.The system of claim 13, wherein the operations further comprise, foreach agent of the plurality of agents: generating a respective featurerepresentation of each agent, comprising: generating one or moreimportance score features of the agent from the output channel;generating one or more additional features of the agent based on sensordata captured by one or more sensors of the vehicle; and generating thefeature representation of the agent from the importance score featuresof the agent and the additional features of the agent; processing thefeature representation of the agent using an importance score refiningmodel to generate a refined importance score for the agent thatcharacterizes an estimated impact of the agent on planning decisionsgenerated by a planning system of the vehicle which plans a futuretrajectory of the vehicle.
 15. The system of claim 12, wherein obtainingthe respective values of each motion parameter in the predetermined setof motion parameters for a previous time point comprises one or more of:obtaining the value of a velocity motion parameter which characterizes avelocity of the vehicle at the previous time point; obtaining the valueof an acceleration motion parameter which characterizes an accelerationof the vehicle at the previous time point; and obtaining the value of aheading motion parameter which characterizes a heading of the vehicle atthe previous time point.
 16. One or more non-transitory computer storagemedia storing instructions that when executed by one or more computerscause the one or more computers to perform operations comprising:processing an input that characterizes a trajectory of a vehicle in anenvironment using an importance scoring model to generate an output thatdefines a respective importance score for each of a plurality of agentsin the environment in the vicinity of the vehicle, wherein theimportance score for an agent characterizes an estimated impact of theagent on planning decisions generated by a planning system of thevehicle which plans a future trajectory of the vehicle; identifying, ashigh-priority agents, a proper subset of the plurality of agents withthe highest importance scores; for only those agents of the plurality ofagents that are identified as high-priority agents, generating datacharacterizing the agents using a first prediction model; and providingthe data characterizing the high-priority agents generated using thefirst prediction model to the planning system of the vehicle to generatethe planning decisions which plan the future trajectory of the vehicle.17. The non-transitory computer storage media of claim 16, wherein theoperations further comprise: obtaining historical data characterizingthe trajectory of the vehicle in the environment, the historical datacomprising, for each of a plurality of previous time points, datadefining: (i) a spatial position in the environment occupied by thevehicle at the previous time point, and (ii) respective values of eachmotion parameter in a predetermined set of motion parameters, whereinthe value of each motion parameter characterizes a respective feature ofa motion of the vehicle at the previous time point; generating arepresentation of the trajectory of the vehicle in the environment,wherein: the representation of the trajectory of the vehicle in theenvironment is a concatenation of a plurality of channels; each channelis represented as a two-dimensional array of data values; each positionin each channel corresponds to a respective spatial position in theenvironment; corresponding positions in different channels correspond tothe same spatial position in the environment; the channels comprise atime channel and a respective motion channel corresponding to eachmotion parameter in the predetermined set of motion parameters; and foreach particular spatial position in the environment occupied by thevehicle at a particular previous time point: the position in the timechannel which corresponds to the particular spatial position defines theparticular previous time point; and for each motion channel, theposition in the motion channel which corresponds to the particularspatial position defines the value of the motion parameter correspondingto the motion channel at the particular previous time point; whereinprocessing an input that characterizes a trajectory of the vehicle inthe environment comprises processing an input that includes therepresentation of the trajectory of the vehicle in the environment. 18.The non-transitory computer storage media of claim 17, wherein: theoutput of the importance scoring model comprises an output channel thatis represented as a two-dimensional array of data values; each positionin the output channel corresponds to a respective spatial position inthe environment; and for each spatial position in the environment thatis occupied by an agent of the plurality of agents at a current timepoint, the position in the output channel that corresponds to thespatial position defines an importance score of the agent.
 19. Thenon-transitory computer storage media of claim 18, wherein theoperations further comprise, for each agent of the plurality of agents:generating a respective feature representation of each agent,comprising: generating one or more importance score features of theagent from the output channel; generating one or more additionalfeatures of the agent based on sensor data captured by one or moresensors of the vehicle; and generating the feature representation of theagent from the importance score features of the agent and the additionalfeatures of the agent; processing the feature representation of theagent using an importance score refining model to generate a refinedimportance score for the agent that characterizes an estimated impact ofthe agent on planning decisions generated by a planning system of thevehicle which plans a future trajectory of the vehicle.
 20. Thenon-transitory computer storage media of claim 17, wherein obtaining therespective values of each motion parameter in the predetermined set ofmotion parameters for a previous time point comprises one or more of:obtaining the value of a velocity motion parameter which characterizes avelocity of the vehicle at the previous time point; obtaining the valueof an acceleration motion parameter which characterizes an accelerationof the vehicle at the previous time point; and obtaining the value of aheading motion parameter which characterizes a heading of the vehicle atthe previous time point.